# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=312

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**Page:** 313

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## [ERROR: LoadError: Unable to locate Gurobi installation](https://discourse.julialang.org/t/error-loaderror-unable-to-locate-gurobi-installation/74051)

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**Author:** [@konsath](https://discourse.julialang.org/u/konsath)\
**Replies:** 2\
**Last updated:** [January 4, 2022, 8:09pm UTC](https://discourse.julialang.org/t/error-loaderror-unable-to-locate-gurobi-installation/74051 "2022-01-04T20:09:50Z")

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I’m using Julia 1.6.5 and Gurobi 9.5.0 but right now Julia is adding an outdated version of Gurobi that doesn’t match my Path (9.5.0). Could anyone provide some insight maybe? :slight\_smile: ‘’’ julia\> Pkg.build(“Gurob…

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## [Chebfun equivalent for differentiation matrices in Julia?](https://discourse.julialang.org/t/chebfun-equivalent-for-differentiation-matrices-in-julia/74042)

<div class="topic-metadata">

**Author:** [@yewalenikhil65](https://discourse.julialang.org/u/yewalenikhil65)\
**Replies:** 4\
**Last updated:** [January 4, 2022, 6:04pm UTC](https://discourse.julialang.org/t/chebfun-equivalent-for-differentiation-matrices-in-julia/74042 "2022-01-04T18:04:12Z")

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Is there yet a differentiation matrices calculating tool in some Julia package ? Something similar to https://github.com/chebfun/chebfun/blob/master/diffmat.m I have tried searching in JuliaApproximation community but c…

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## [Setting up Julia on Spark on AWS EMR](https://discourse.julialang.org/t/setting-up-julia-on-spark-on-aws-emr/63781)

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**Author:** [@Sumit\_Malbari](https://discourse.julialang.org/u/Sumit_Malbari)\
**Replies:** 24\
**Last updated:** [January 4, 2022, 3:13pm UTC](https://discourse.julialang.org/t/setting-up-julia-on-spark-on-aws-emr/63781 "2022-01-04T15:13:50Z")

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Hi folks, I want to use Julia on Spark on AWS EMR as this is one of the requirement at my workplace. I tried to follow the steps from Julia & Spark but I was not able to succeed. If anyone has implemented it on AWS EM…

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## [LP Warm Starts - using Gurobi with JuMP](https://discourse.julialang.org/t/lp-warm-starts-using-gurobi-with-jump/73840)

<div class="topic-metadata">

**Author:** [@bjr221](https://discourse.julialang.org/u/bjr221)\
**Replies:** 6\
**Last updated:** [January 3, 2022, 11:48pm UTC](https://discourse.julialang.org/t/lp-warm-starts-using-gurobi-with-jump/73840 "2022-01-03T23:48:32Z")

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Is there any way to warm start (choose initial vertex for dual simplex algorithm) for a linear program that you’ve created? I have tried using the “PStart” attribute for LPs to no avail, and the “.start” attribute is for…

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## [No method matching get\_connection\_type when connecting components](https://discourse.julialang.org/t/no-method-matching-get-connection-type-when-connecting-components/73990)

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**Author:** [@jenrei](https://discourse.julialang.org/u/jenrei)\
**Replies:** 1\
**Last updated:** [January 4, 2022, 10:12am UTC](https://discourse.julialang.org/t/no-method-matching-get-connection-type-when-connecting-components/73990 "2022-01-04T10:12:31Z")

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Hello, I’m trying to get a feeling for MTK by converting the electric circuit example for acasual component based modeling to thermal components. Unfortunately I get this error when I’m using connect: ht\_eqs = \[ co…

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## [Delaunay Triangularization](https://discourse.julialang.org/t/delaunay-triangularization/36172)

<div class="topic-metadata">

**Author:** [@Donald\_Lacombe](https://discourse.julialang.org/u/Donald_Lacombe)\
**Replies:** 20\
**Last updated:** [January 4, 2022, 1:55am UTC](https://discourse.julialang.org/t/delaunay-triangularization/36172 "2022-01-04T01:55:26Z")

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Hello! I’d like to be able to obtain the following output from MATLAB but in Julia. Here is a toy example in MATLAB: \>\> x = rand(5,1) x = 0.8147 0.9058 0.1270 0.9134 0.6324 \>\> y = rand(5,1) y = …

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## [MLP - DimensionMisMatch Error Just Before Training](https://discourse.julialang.org/t/mlp-dimensionmismatch-error-just-before-training/74007)

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**Author:** [@sherlock\_holmes](https://discourse.julialang.org/u/sherlock_holmes)\
**Replies:** 2\
**Last updated:** [January 3, 2022, 10:57pm UTC](https://discourse.julialang.org/t/mlp-dimensionmismatch-error-just-before-training/74007 "2022-01-03T22:57:21Z")

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Hi, I’m trying to train a MLP model to predict number of real roots of polynomials. x\_train and y\_train include array of arrays such as \[\[-204, 20, 13, 1, 0\]\] which are coefficients of polynomials. x\_test and y\_test incl…

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## [CUDA on Julia 1.7 giving wrong results](https://discourse.julialang.org/t/cuda-on-julia-1-7-giving-wrong-results/73997)

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**Author:** [@shiroghost](https://discourse.julialang.org/u/shiroghost)\
**Replies:** 5\
**Last updated:** [January 3, 2022, 9:31pm UTC](https://discourse.julialang.org/t/cuda-on-julia-1-7-giving-wrong-results/73997 "2022-01-03T21:31:47Z")

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Hi all, I have a fairly complex code that has worked well with julia 1.5 - 1.6. I have tried to run this with te latest julia 1.7, and the code runs, but produces wrong results. This is the list of packages used, in cas…

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## [Filter date from a feather DataFrame JULIA](https://discourse.julialang.org/t/filter-date-from-a-feather-dataframe-julia/73993)

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**Author:** [@SamanthaCassab](https://discourse.julialang.org/u/SamanthaCassab)\
**Replies:** 4\
**Last updated:** [January 3, 2022, 9:01pm UTC](https://discourse.julialang.org/t/filter-date-from-a-feather-dataframe-julia/73993 "2022-01-03T21:01:54Z")

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Hi, I want to filter my DataFrame by Date, but the column wich has the date has the following type: Typeof(DateTime("2021-12-17T06:00:00")) Feather.Arrow.Timestamp{Microsecond} The column look like: DateTime("2020-12…

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## [Syntax for indicator constraints](https://discourse.julialang.org/t/syntax-for-indicator-constraints/73716)

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**Author:** [@JohnZ](https://discourse.julialang.org/u/JohnZ)\
**Replies:** 4\
**Last updated:** [January 3, 2022, 7:41pm UTC](https://discourse.julialang.org/t/syntax-for-indicator-constraints/73716 "2022-01-03T19:41:37Z")

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I have a model with two constraints. The first constraint is a big M constraint, which I am trying to reformulate as an indictor constraint. I have tried to follow the syntax given in the documentation, but I don’t get a…

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## [JuMP: constraint to use a value only \`n\` times](https://discourse.julialang.org/t/jump-constraint-to-use-a-value-only-n-times/73930)

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**Author:** [@Sushant-Padha](https://discourse.julialang.org/u/Sushant-Padha)\
**Replies:** 5\
**Last updated:** [January 3, 2022, 7:38pm UTC](https://discourse.julialang.org/t/jump-constraint-to-use-a-value-only-n-times/73930 "2022-01-03T19:38:41Z")

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I am trying to solve a problem using ConstraintSolver.jl which uses JuMP. I want to define a constraint for a group of variables, such that certain values are only chosen certain times. For eg: if the variables are 1 \<=…

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## [LSTM with batch vs with individual values](https://discourse.julialang.org/t/lstm-with-batch-vs-with-individual-values/73722)

<div class="topic-metadata">

**Author:** [@ForceBru](https://discourse.julialang.org/u/ForceBru)\
**Replies:** 4\
**Last updated:** [January 3, 2022, 10:37am UTC](https://discourse.julialang.org/t/lstm-with-batch-vs-with-individual-values/73722 "2022-01-03T10:37:37Z")

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Looks like there are two ways of calling models (running forecasting/regression/etc) in Flux: “batch mode” (model(data\_matrix)) and “vector comprehension mode” (\[model(elem)\[1\] for elem in data\_vector\]), where elem is on…

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## [\[ANN\] MuseInference.jl (drop-in replacement for HMC / VI, try it on your problem!)](https://discourse.julialang.org/t/ann-museinference-jl-drop-in-replacement-for-hmc-vi-try-it-on-your-problem/73468)

<div class="topic-metadata">

**Author:** [@marius311](https://discourse.julialang.org/u/marius311)\
**Replies:** 4\
**Last updated:** [January 3, 2022, 7:40am UTC](https://discourse.julialang.org/t/ann-museinference-jl-drop-in-replacement-for-hmc-vi-try-it-on-your-problem/73468 "2022-01-03T07:40:28Z")

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Earlier this week we put out a paper describing a new method for hierarchical Bayesian inference we dubbed the Marginal Unbiased Score Expansion (MUSE), which can pretty drastically outperform HMC / VI for a wide class o…

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## [Is it possible that numerical optimisation solve time decreases for some range of dimensions from low to moderate levels?](https://discourse.julialang.org/t/is-it-possible-that-numerical-optimisation-solve-time-decreases-for-some-range-of-dimensions-from-low-to-moderate-levels/73857)

<div class="topic-metadata">

**Author:** [@iHany](https://discourse.julialang.org/u/iHany)\
**Replies:** 11\
**Last updated:** [January 3, 2022, 4:07am UTC](https://discourse.julialang.org/t/is-it-possible-that-numerical-optimisation-solve-time-decreases-for-some-range-of-dimensions-from-low-to-moderate-levels/73857 "2022-01-03T04:07:00Z")

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Hi, I encountered a weird phenomenon of solve time calculation in numerical optimisation. Backgrounds There is a bunch of approximators, \\{ f\_j \\}\_{j \\in J}. For example, f\_1 is a feedforward (dense) neural network, an…

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## [ModelingToolkit second derivative only gives first derivative](https://discourse.julialang.org/t/modelingtoolkit-second-derivative-only-gives-first-derivative/70703)

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**Author:** [@ctessum](https://discourse.julialang.org/u/ctessum)\
**Replies:** 2\
**Last updated:** [January 3, 2022, 3:31am UTC](https://discourse.julialang.org/t/modelingtoolkit-second-derivative-only-gives-first-derivative/70703 "2022-01-03T03:31:47Z")

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Hello, I’m running into an issue that has left me confused. Using ModelingToolkit v6.7.1, I (for example) want to simulate a falling object. So: @variables t \[unit = u"s"\] x(t) \[unit = u"m"\] v(t) \[unit = u"m/s"\] @param…

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## [Optimize many non linear functions](https://discourse.julialang.org/t/optimize-many-non-linear-functions/73761)

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**Author:** [@jmmshn](https://discourse.julialang.org/u/jmmshn)\
**Replies:** 4\
**Last updated:** [January 2, 2022, 8:44pm UTC](https://discourse.julialang.org/t/optimize-many-non-linear-functions/73761 "2022-01-02T20:44:06Z")

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I’m tying optimize the sum of series objective functions in funcs using the Ipot optimizer A minimal example shown below show result in an optimal objective value of 5. However it current returns objective\_value(model)…

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## [(JuMP+NLopt) Only initial value returned without error warning](https://discourse.julialang.org/t/jump-nlopt-only-initial-value-returned-without-error-warning/73074)

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**Author:** [@RunguangLi](https://discourse.julialang.org/u/RunguangLi)\
**Replies:** 7\
**Last updated:** [January 2, 2022, 8:40pm UTC](https://discourse.julialang.org/t/jump-nlopt-only-initial-value-returned-without-error-warning/73074 "2022-01-02T20:40:31Z")

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For a nonlinear optimization problem with 9 parameters, calling Ipopt works well, while calling NLopt only returns the initial value without any error warning. Could someone tell me how to correct it? Using NLopt: usin…

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## [Noobish question regarding yhat probabilities](https://discourse.julialang.org/t/noobish-question-regarding-yhat-probabilities/73905)

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**Author:** [@AdamWysokinski](https://discourse.julialang.org/u/AdamWysokinski)\
**Replies:** 3\
**Last updated:** [January 2, 2022, 11:26am UTC](https://discourse.julialang.org/t/noobish-question-regarding-yhat-probabilities/73905 "2022-01-02T11:26:00Z")

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Hi, I’ve just started learning MLJ and I’m recreating a RandomForrect-based binary classification that I did in Python/Scikit. The MLJ version works fine, with one major exception.When I put new data through the trained…

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## [Convergence of a BVProblem with a Saddle Structure](https://discourse.julialang.org/t/convergence-of-a-bvproblem-with-a-saddle-structure/73678)

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**Author:** [@ptoche](https://discourse.julialang.org/u/ptoche)\
**Replies:** 1\
**Last updated:** [January 2, 2022, 10:14am UTC](https://discourse.julialang.org/t/convergence-of-a-bvproblem-with-a-saddle-structure/73678 "2022-01-02T10:14:05Z")

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The following two-point boundary value problem is difficult to solve because the stationary state has a saddle structure, with one positive and one negative eigenvalue: only one path leads to the stationary state — all o…

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## [How to efficiently and precisely fit a function with neural networks?](https://discourse.julialang.org/t/how-to-efficiently-and-precisely-fit-a-function-with-neural-networks/73726)

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**Author:** [@thorek1](https://discourse.julialang.org/u/thorek1)\
**Replies:** 16\
**Last updated:** [January 1, 2022, 1:50pm UTC](https://discourse.julialang.org/t/how-to-efficiently-and-precisely-fit-a-function-with-neural-networks/73726 "2022-01-01T13:50:36Z")

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Hi, I am trying (and failing in terms of precision) to use neural networks to fit stochastic optimal control problems. Since this problem has many parts and I would like to have 1e-6 precision I went back to something m…

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## [What is the correct way to regex route parameters in Genie.jl?](https://discourse.julialang.org/t/what-is-the-correct-way-to-regex-route-parameters-in-genie-jl/68064)

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**Author:** [@Matrsz](https://discourse.julialang.org/u/Matrsz)\
**Replies:** 0\
**Last updated:** [September 12, 2021, 11:22pm UTC](https://discourse.julialang.org/t/what-is-the-correct-way-to-regex-route-parameters-in-genie-jl/68064 "2021-09-12T23:22:58Z")

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I’m trying to use a regex for one of the fields in a web app’s route. The route requires a lot of dynamic routing. My issue resides in the fact that the regex field is not the last field in my route, and I realized that …

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## [Using a linear combination of dataframe columns as a functional input](https://discourse.julialang.org/t/using-a-linear-combination-of-dataframe-columns-as-a-functional-input/73834)

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**Author:** [@jdhooghe](https://discourse.julialang.org/u/jdhooghe)\
**Replies:** 0\
**Last updated:** [December 30, 2021, 8:13pm UTC](https://discourse.julialang.org/t/using-a-linear-combination-of-dataframe-columns-as-a-functional-input/73834 "2021-12-30T20:13:16Z")

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Hello, I have a dataframe whose column names represent polynomial portions such as ‘xy’ and as such, are symbols. I want to take all of these column names, which include: :x :y :xy :xx :yy and add them together us…

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## [LogNormal-Distribution - how to set mu and sigma](https://discourse.julialang.org/t/lognormal-distribution-how-to-set-mu-and-sigma/7101)

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**Author:** [@LotteVictor](https://discourse.julialang.org/u/LotteVictor)\
**Replies:** 17\
**Last updated:** [December 30, 2021, 3:20pm UTC](https://discourse.julialang.org/t/lognormal-distribution-how-to-set-mu-and-sigma/7101 "2021-12-30T15:20:08Z")

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Hey there! I’m trying to draw random numbers from a Log-Normal distribution with a given mean and standard-deviation. As far as i know, the LogNormal(\\mu \\sigma) lets you set the mean and standard deviation of the distri…

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## [Docs DifferentialEquations.jl SecondOrderODEProblem](https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773)

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**Author:** [@ziolai](https://discourse.julialang.org/u/ziolai)\
**Replies:** 1\
**Last updated:** [December 30, 2021, 11:14am UTC](https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773 "2021-12-30T11:14:10Z")

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What does the symbol f (as opposed to f1 or f2) in SecondOrderODEProblem{isinplace}(f,du0,u0,tspan,p=NullParameters();kwargs…) on the page Dynamical, Hamiltonian, and 2nd Order ODE Solvers · DifferentialEquations.jl re…

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## [Continuous analog of SavingCallback from DifferentialEquations.jl](https://discourse.julialang.org/t/continuous-analog-of-savingcallback-from-differentialequations-jl/73613)

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**Author:** [@EvgenijGr](https://discourse.julialang.org/u/EvgenijGr)\
**Replies:** 7\
**Last updated:** [December 29, 2021, 4:52pm UTC](https://discourse.julialang.org/t/continuous-analog-of-savingcallback-from-differentialequations-jl/73613 "2021-12-29T16:52:33Z")

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So, the problem that I wanted to solve is the following. For a system that I study I wanted to record time and phase state when F(x, t) = 0, where F(x, t) is some non-linear function. If F(x, t) is linear, then there is …

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## [Flux "60 minute blitz" weird error when using GPU](https://discourse.julialang.org/t/flux-60-minute-blitz-weird-error-when-using-gpu/73537)

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**Author:** [@GlenHenshaw](https://discourse.julialang.org/u/GlenHenshaw)\
**Replies:** 10\
**Last updated:** [December 29, 2021, 8:58am UTC](https://discourse.julialang.org/t/flux-60-minute-blitz-weird-error-when-using-gpu/73537 "2021-12-29T08:58:26Z")

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I’m running the following Flux code, which comes directly from the Flux “60 Minute Blitz” tutorial. I get a weird error when using the |\> gpu construct, but not when the code runs on the CPU. I’ve posted this as a bug to…

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## [Reading png rgb channels, Julia vs Python](https://discourse.julialang.org/t/reading-png-rgb-channels-julia-vs-python/73599)

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**Author:** [@t-bltg](https://discourse.julialang.org/u/t-bltg)\
**Replies:** 13\
**Last updated:** [December 28, 2021, 6:43pm UTC](https://discourse.julialang.org/t/reading-png-rgb-channels-julia-vs-python/73599 "2021-12-28T18:43:01Z")

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So here is a very simple 8x8 png image: Opening it in GIMP: So this pixel has RGBA(233, 173, 4, 244) components. Using Python: import imageio img = imageio.imread('img.png') r = img\[:, :, 0\] g = img\[:, :, 1\] b =…

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## [CUDA porting to shift-inverse eigenvalues](https://discourse.julialang.org/t/cuda-porting-to-shift-inverse-eigenvalues/73691)

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**Author:** [@albertomercurio](https://discourse.julialang.org/u/albertomercurio)\
**Replies:** 0\
**Last updated:** [December 28, 2021, 12:26am UTC](https://discourse.julialang.org/t/cuda-porting-to-shift-inverse-eigenvalues/73691 "2021-12-28T00:26:22Z")

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The Arpack eigenvalues solver is very fast. With a 100000x100000 sparse matrix, I can get a few eigenvalues with the shift-invert method in 20-30 seconds approximately! Since I always want the best performances, I wonde…

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## [Trying to understand CUDA benchmark](https://discourse.julialang.org/t/trying-to-understand-cuda-benchmark/73639)

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**Author:** [@Jakub\_Mitura](https://discourse.julialang.org/u/Jakub_Mitura)\
**Replies:** 1\
**Last updated:** [December 28, 2021, 8:33am UTC](https://discourse.julialang.org/t/trying-to-understand-cuda-benchmark/73639 "2021-12-28T08:33:30Z")

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I am benchmarking my kernel that is relatively simple it iterates over 2 arrays of the same size and accumulates in local variables times both arrays agree or not warp reduction of local variables thread block reductio…

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## [Package install on (offline) Cluster - Build needs internet](https://discourse.julialang.org/t/package-install-on-offline-cluster-build-needs-internet/19862)

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**Author:** [@JonasIsensee](https://discourse.julialang.org/u/JonasIsensee)\
**Replies:** 7\
**Last updated:** [December 28, 2021, 7:25am UTC](https://discourse.julialang.org/t/package-install-on-offline-cluster-build-needs-internet/19862 "2021-12-28T07:25:10Z")

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Hey everyone, I’m trying to use julia 1.0 on our cluster. It is not connected to the internet (login via login-server) so I can’t use the standard procedure to install the packages I need. I read here that one option…

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